What does it mean by "completing the square" and how do u do it?

Completing the square goes back to pythagorean thm
but the way u do it, u want to find a value that enable u to take sqrt of both sides and solve
x^2-8x+3=0
x^2-8x=-3
we need (x-4)^2 so add 16
(x-4)^2=-3+16
(x-4)^2=13
x-4=sqrt13
x=4(+/-)sqrt13

Option ait states the correct answer

What class is this? i have no idea and i'm not going to give you the wrong answer. do you have a graph that goes with all the questions